This invention is in the field of 35mm slide photography, and particularly the procedures and apparatus for exposing 35mm film to be used in making slides for multi-image projection.
Slide photography has developed from the early and still used simple slides made with carboard mounts for a single frame of 35mm film, to the pin-registered Wess mounts which are plastic envelopes for holding a single frame of 35mm film in precise location and orientation relative to the sprocket holes in the film and the edges of the envelope. The slides made with cardboard mounts are typically loaded in a slide projector to project one image at a time on a screen or a wall. During the steps of exposing the film for these slides, securing the film in the cardboard mounts, positioning the slides in a projector, and projecting the images, there was no concern about the positional relationship of each frame of film to the camera's film aperture, to the slide mount, the projector, or the screen, because for each frame and slide there is produced only a single image, with no need to accurately locate or align that image relative to any other image.
More recently slide photography has become more popular as a sales and promotional medium for business, industry and education, in addition to its use in entertainment, and new sophisticated photographic techniques evolved. These techniques include using two or more projectors to produce a composite image comprising adjacent images from the separate projectors, producing a series of different single images in the same location by different projectors operating at different times, the apparatus for this latter technique called a dissolving system when one image dissolves as the next appears, and providing other programmable multi-imaging slide shows. This led to the popular formats of two or three adjacent screens and one bank of multiple projectors for each screen.
With these techniques there is one basic problem; when one projected image is placed adjacent another, and these images are segments of a single art work, there may not be sufficient registration of mating lines on the screen for the result to be usable, saleable, and/or aesthetically satisfying. Any lack of registration in the slides becomes vastly magnified in the projected images, and in the normal cardboard mounted slides, the film is merely approximately positioned and adhered in place with no particular registration relationship established between film, the camera, the projector, and other images on the screen.
A development which significantly reduced the registration problem was the Wessinger or Wess mount for slides. This is a plastic envelope having its own registration projections or pins for entering sprocket holes of a film frame to align it exactly as it was aligned in the camera relative to the center of the film aperture. When a Wess mount is placed in a projector its side edges establish reference surfaces whereby the registration of the film in the camera is effectively transferred or converted to a corresponding registration in the projector. This Wess mount system became the standard in the industry and made possible the great development of multi-image slide work now used by corporate, educational, and advertising media centers.
While the Wess mounts provided the necessary precision for transferring pin registration from the film to the mount and thence to the projector and to the screen, the overall photographic technique required the original film to be in equally precise registration in the camera. To provide such film registration in the camera there have been developed production slide film cameras such as animation film strip cameras, or alternatively custom-made cameras having accurate film registration means. Unfortunately these cameras cost between $15,000 and $45,000 each, which is far too expensive for the many small and medium-sized media centers who do or could produce the multi-image slide work now growing in popularity. Without their own in-house production or custom pin-registered cameras, these media people have the problems of transporting their art work and personnel to often inconveniently located production centers, paying expensive fees, and perhaps the worst problem, experiencing uncontrollable and intolerable delays in their production schedules.
Attempts have been made to use the far cheaper, smaller, and widely available single lens reflex 35mm cameras (SLRs); however their registration means is limited to the drive sprocket pins which are simply too imprecise for multi-imaging work. As is well known, these sprocket teeth enter sprocket holes in the film and as the sprocket rotates the film is advanced. A more careful examination reveals that the sprocket tooth dimensions are necessarily much smaller than the sprocket hole dimensions in the film because the teeth approach the holes at an oblique angle and much clearance is needed in these ultra-compactly designed SLR cameras; still further clearance is provided to compensate for variable shrinkage that occurs in the film and alters the distances between sprocket holes. Consequently sprocket teeth dimensions cannot even closely approximate sprocket hole dimensions, and since this is essentially the only registration means in SLRs, these cameras simply do not have the capability for registration of the Wess mounts in the magnitude required for multi-image slide work.
The present invention represents a solution to the problem of the media people, at a time when the problem is becoming more severe due to greatly increased demand for precision slide work, escalating costs of production and custom cameras, and a trend for even more sophisticated and expensive cameras designed especially and solely to produce precisely pin-registered slides.
These expensive and limited-use custom cameras typically have very large diameter sprocket drives for registering and advancing the film, or there are pin registration techniques, such as a moving cam-driven part having fixed pins which enter film sprocket holes and lift the film off the film aperture and in a rotating fashion advance and place the film, frame-by-frame. These cameras, in addition to being large and non-portable, are expensive and restricted to this particular use, which would unreasonably tie up capital for the limited budget small media offices. Finally, it has been determined that the structural features of these production and custom cameras are not adjustable to miniaturization and cannot be transferred into the small SLR cameras whose compact design has absolutely no additional space for a larger drive sprocket, or moving cam elements as described in the custom cameras.
A solution to these problems has been found as will be summarized below, followed by a detailed description of the preferred embodiment of our new invention.